In a common method for repairing a die-casting metal mold upon a crack occurring therein, as shown in FIG. 8, a large part of the metal mold surrounding the crack is removed by means of a cutting tool, the part where the removal has been performed is subjected to build-up welding, and then subjected to surface finishing.
As an improvement of the aforementioned common repair method, Patent Document 1 discloses performing build-up welding while melting powder for metal mold repair by means of a plasma arc. As the powder for metal mold repair, Patent Document 1 proposes an alloy powder consisting of a total 10 wt % or less of a carbide consisting of at least one of NbC, VC and WC, and the balance of a Ni—Cr—Mo-based heat resistant alloy.
Also, Patent Document 2 discloses applying a coating material, which has been prepared by dispersing metal powder in a solvent, to a base metal and heating the base metal to diffuse the metal in the base metal, and more specifically, it proposes: selecting at least one of Cu and Mn as an element to be diffused in the case where the base metal is a Zn alloy; selecting Cr in the case where the base metal is an Fe alloy; selecting at least one of Al, Cr, Ni and N in the case where the base metal is a Ti alloy; and selecting Ni in the case where the base metal is a Cu alloy.
Patent Document 1: Japanese Patent Laid-Open No. 2005-97743
Patent Document 2: Japanese Patent Laid-Open No. 2004-68047
In the method disclosed in Patent Document 1, when a crack is repaired, as in the conventional method, a part of the metal mold including the crack is cut off, and build-up welding is performed on the part where the cutting has been performed. Where build-up welding is performed, what is called secondary cracking, i.e., a crack occurring again in a part that is somewhat outside the part where the build-up welding has been performed, is prone to occur due to a thermal effect caused by the welding.
Also, in the conventional method, in some cases, a cutting tool cannot be used depending on the part where a crack occurs. In this case it takes a lot of trouble and time for repair.
Meanwhile, the content disclosed in Patent Document 2 makes it possible to improve the properties of the base metal surface, but cannot be applied to repairing a crack in a metal mold because the coating material itself does not become an alloy by means of thermal treatment.